1. Field of the Invention
The invention is related to enhanced oil production. More particularly, the invention relates to a method and apparatus for controlling injection wells to optimize production from associated production wells.
2. Prior Art
Injection wells have, of course, been employed for many years in order to flush residual oil in a formation toward a production well and increase yield from the area. A common injection scenario is to pump steam down an injection well and into the formation which functions both to heat the oil in the formation and force its movement through the practice of steam flooding. In some cases, heating is not necessary as the residual oil is in a flowable form, however in some situations the oil is in such a viscous form that it requires heating in order to flow. Thus, by using steam one accomplishes both objectives of the injection well: 1) to force residual oil toward the production well and 2) to heat any highly viscous oil deposits in order mobilize such oil to flow ahead of the flood front toward the production well.
As is well known to the art, one of the most common drawbacks of employing the method above noted with respect to injection wells is an occurrence commonly identified as xe2x80x9cbreakthroughxe2x80x9d. Breakthrough occurs when a portion of the flood front reaches the production well. As happens the flood water remaining in the reservoir will generally tend to travel the path of least resistance and will follow the breakthrough channel to the production well. At this point, movement of the viscous oil ends. Precisely when and where the breakthrough will occur depends upon water/oil mobility ratio, the lithology, the porosity and permeability of the formation as well as the depth thereof. Moreover, other geologic conditions such as faults and unconformities also affect the in-situ sweep efficiency.
While careful examination of the formation by skilled geologists can yield a reasonable understanding of the characteristics thereof and therefore deduce a plausible scenario of the way the flood front will move, it has not heretofore been known to monitor precisely the location of the flood front as a whole or as individual sections thereof. By so monitoring the flood front, it is possible to direct greater or lesser flow to different areas in the reservoir, as desired, by adjustment of the volume and location of both injection and production, hence controlling overall sweep efficiency. By careful control of the flood front, it can be maintained in a controlled, non fingered profile. By avoiding premature breakthrough the flooding operation is effective for more of the total formation volume, and thus efficiency in the production of oil is improved.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the electronically controlled injection well system of the invention.
The invention provides significantly more information to well operators thus enhancing oil recovery to a degree not heretofore known. This is accomplished by providing real time information about the formation itself and the flood front as well as the produced fluid by providing permanent downhole sensors capable of sensing changes in the swept and unswept formation and/or the progression of the flood front and/or changes in the produced fluid (e.g. temperature). Preferably, a plurality of sensors would be employed to provide information about discrete portions of strata surrounding the injection well. This provides a more detailed data set regarding the well(s) and surrounding conditions. The sensors are, preferably, connected to a processor either downhole or at the surface for processing of information. Moreover, in a preferred embodiment the sensors are connected to computer processors which are also connected to sensors in a production well (which are similar to those disclosed in U.S. Pat. No. 5,597,042 which is fully incorporated herein by reference) to allow the production well to xe2x80x9ctalkxe2x80x9d directly to the related injection well(s) to provide an extremely efficient real time automatic operation. Sensors employed will be to sense temperature, pressure, flow rate, electrical and acoustic conductivity, density, strain and to detect various light transmission and reflection phenomena. All of these sensor types are available commercially in various ranges and sensitivities which are selectable by one of ordinary skill in the art depending upon particular conditions known to exist in a particular well operation. Specific pressure measurements will also include pressure(s) at the exit valve(s) down the injection well or injection zone in a single well and at the pump which may be located downhole or at the surface. Measuring said pressure at key locations such as at the outlet, upstream of the valve(s) near the pump, etc., will provide information about the speed, volume, direction, etc. at/in which the waterflood front (or other fluid) is moving. Large differences in the pressure from higher to lower over a short period of time could indicate a breakthrough. Conversely, pressure from lower to higher over short periods of time could indicate that the flood front had hit a barrier. Similarly, a rapid temperature rise in the produced fluid in one zone of the production well can indicate imminent breakthrough. These conditions are, of course, familiar to one of skill in the art but heretofore far less would have been known since no workable system for measuring the parameters existed. Therefore, the present invention, since it increases knowledge, and automation, it increases productivity.
Referring now to the measurement of density as noted above, the present invention uses fluid densities to monitor the flood front from the trailing end. As will be appreciated from the detailed discussion herein, the interface between the flood front and the hydrocarbon fluid provides an acoustic barrier upon which a signal can be bounced. Thus, by generating acoustic signals and mapping the reflection, the profile of the front is generated in 4D i.e., three dimensions over time.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.